Brake device and method for operating a brake device

ABSTRACT

The invention relates to a brake device and a method for operating a brake device, wherein said brake device comprises an actuation device, also a booster device, in particular having an electro-hydraulic drive, a piston cylinder device (main cylinder) in order to supply hydraulic pressure medium to the brake circuits, a valve device for controlling or regulating the supply of the pressure medium and an electronic control or regulating device. According to the invention provision is made for additional pressure medium volume to be supplied in a controlled manner to at least one brake circuit by means of a further piston cylinder device, in particular a double stroke piston and at least one valve controlled by the control or regulating device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/022,394, filed Mar. 16, 2016 as a Section 371 U.S. National StageFiling of International Application No. PCT/EP2014/069650, filed Sep.16, 2014, which was published in the German language on Mar. 19, 2015,under International Publication No. WO 2015/036601 A2, which claimspriority to German Patent Application No. 10 2013 110 188.7, filed onSep. 16, 2013, German Patent Application No. 10 2013 111 974.3, filed onOct. 30, 2013, and German Patent Application No. 10 2014 102 536.9,filed on Feb. 26, 2014, the disclosures of all of which are incorporatedby reference herein.

FIELD OF ENDEAVOR

The invention relates to a brake device or an actuation device and to amethod for operating a brake device.

PRIOR ART

The requirements for brake systems are increasing. This also applies, inparticular with regard to fail-safety and a good fallback level. If thebrake force booster fails, then a deceleration that is, if possible,greater than 0.64 g should be achieved with the internationallypredetermined foot force of 500 N which means notably more compared withthe minimum requirement of the legislator of 0.24 g. An advantage of thelong deceleration that can be achieved is also that a red warning light,which irritates the driver, does not have to be actuated.

This requirement can be resolved by brake-by-wire systems with travelsimulator. In this connection, the main cylinder (HZ) or tandem maincylinder (THZ) is configured for the fallback level in the case of thebrake system failing. This takes place through correspondingdimensioning with a small diameter. Greater pressures thereby result inthe case of a corresponding foot force. The required volume for 0.64 gand corresponding pressure is relatively small in comparison to themaximum pressure in the case of complete vehicle deceleration andfading. A THZ cannot fully apply the required volume even in the case ofa larger stroke. In DE 10 2007 062839 from the applicant, a solutiontherefor with a storage chamber is proposed, which injects correspondingvolumes into the brake circuit in the case of higher pressures.Furthermore, in DE 10 2011 009059 from the applicant, a further solutionis described, in which volume is delivered by the HZ from the reservoirinto the brake circuit via correspond valve and HZ control. In the caseof vehicles with large volume uptake, e.g. SUVs and small vans, thefilling of the brake circuits must necessarily take place when brakingeven before the locking pressure for high p. Both solutions place agreat demand on the leak-tightness of the valves. However, aninterruption of the pressure build-up and low braking distance loss arelinked for the additional filling of the brake circuits.

In DE 10 2011 111368 from the applicant, a system with additionalpistons is described, which provide the required pressure medium volumeand have the advantage of being actuated by the motor spindle and notbeing effective in the fallback level, i.e. they enable thepredetermined deceleration. The correspondingly greater forces maydisadvantageously have an effect here, as they burden the spindle, theball screw drive (KGT) and the bearings.

OBJECT OF THE INVENTION

The object underlying the invention is to provide an improved actuationdevice, in particular for a vehicle brake system, which, in particularalso in a simple manner, enables sufficient pressure fluid volume, inparticular for brake activation.

Achievement of the Object

The achievement of the object according to the invention may be achievedwith the features of as found in the various attached claims.

Advantages of the Invention

With the solution according to the invention and the configurationsthereof, an actuation device, in particular for a vehicle brake, isprovided, by means of which sufficient fluid volume is made available inparticular for brake activation in a surprisingly simple manner. Thiscan take place in a very advantageous manner without notable delay inthe pressure build-up with warning of the fail-safety and possibility todiagnose the fault.

A basic concept of the invention is the formation of the driven pistonof the piston cylinder unit, in particular as a stepped double strokepiston, which builds up the pressure in the piston cylinder unit orHZ/THZ in the part facing the pressure chamber as a conventionalcylindrical piston as usual in the prestroke and in the return stroke,in particular operates as an annular piston and in particular similarlydelivers volume into one or both brake circuits.

With the use according to the invention of a double stroke piston (as itis known per se e.g. from DE 10 2011 007672A1), volume can theoreticallybe delivered into the brake circuits with a high dynamic in an unlimitedmanner. In this regard, the switching of the piston movement by adynamic motor is favoured such that this phase in the temporal pressurebuild-up means only one interruption of a few ms.

Further advantageous embodiments or configurations of the inventionemerge from the features of the further claims to which reference ismade here for descriptive purposes for the sake of simplicity.

The volume control expediently takes place via solenoid valves withoutthe usual check valves.

These solenoid valves for volume control are safety-critical and can befully diagnosed in operation. Additional variants of the valve controlare also conceivable, as is described below.

Different valve connections for the ABS pressure control are alsoconceivable. In addition to the simple and advantageous pressure controlvia multiplexing methods (MUX), as is described further e.g. in EP06724475 from the applicant, the conventional valve connection withinlet and outlet valves can also be used. The rest of the system designcorresponds to the design described in DE 10 2013 105377 and DE 10 2010045617 from the applicant.

The volume control can advantageously be used both for brake boosting(BKV) and also for ABS.

The solenoid valves (EA) can expediently also be used for additionalfunctions, such as pressure reduction from the brake circuits without HZpiston movement for special functions such as for example in the case ofrecuperation or jamming spindle drive, amongst others.

A separation of the spindle from the driven piston is expedient for thefull use of the fallback level. This can take place, e.g. by means of acoupling, as is described in EP 07819692 from the applicant. Referenceis hereby made thereto.

Brake devices are regularly mounted on the bulkhead of the vehicle andprotrude, on the one hand, into the foot space to connect with the brakepedal and on the other hand into the motor compartment. In the case ofleakage from seals in the brake device, fluid can leak into both areas,which must be avoided.

An expedient embodiment of the brake actuation device thus makesprovision so that leakage fluid cannot get through to the outside. Inthis connection, the housing, in particular the motor housing isenlarged and used as a collecting vessel. The escaping leakage fluid isdetected in corresponding quantity by the level sensor of the reservoir.The sensor is advantageously connected to the adjacent ECU.Alternatively, an electrode can also be used in the collecting vessel,which detects even smaller fluid quantities at an early stage. In orderto avoid sloshing of the fluid, corresponding separation chambers with asponge can be used.

The structural length of the actuation device is crucial for futurebrake systems. In the case of integrated solutions, so-called “1-boxconcepts”, a distinction is made between serial and parallel systems,wherein high requirements are placed on the fail-safety andcontrollability of the faults in the e.g. changed pedal characteristicsin the fallback level. In the case of future vehicles, the friction ofthe brake shoes, which cause up to 300 W of power loss and thus CO₂,should be avoided.

A number of measures, e.g. increased rollback sealing in the brakepiston, enable a low-friction brake. The free travel caused thereby forapplying the brake shoes should be maintained as low as possible in itseffect on the brake pedal.

Advantageous embodiments of the invention thus relate to an improvedactuation device, in particular for providing a vehicle brake systemwhich, in particular also in a simple manner, enables sufficientpressure fluid volume, in particular for brake activation. Moreover, thestructural length should to be as short as possible. The system shouldbe usable in the packaging flexibly both for serial and parallel systemsin the so-called compact design. For low-friction brakes with increasedrollback, the pedal travel loss should be as low as possible.

As a result of the larger effective areas of the double stroke piston,in particular in the case of braking and high piston speed, a relativehigh flow quantity occurs, in the case of which negative pressure cannotoccur on the rear side of the piston. Accordingly, suction valves areadvantageously arranged for both piston sides.

A reduction of the structural length can be achieved by concentricarrangement of driven pistons and in particular double stroke pistonsconfigured as annular pistons (as depicted by way of example in FIG. 10of the drawing). Further possibilities consist of the arrangement of thefloating piston parallel to the driven piston or double stroke piston(as depicted for example in FIG. 11 of the drawing) or of thearrangement of the double stroke piston parallel to the main cylinder,in particular with auxiliary pistons. A further variant consists ofusing the rear side of the driven piston similarly for volume deliverywith corresponding valve connection and coupling to the spindle (asdepicted for example in FIG. 13, 13 a of the drawing).

The double stroke piston can, due to the larger piston effective areasthereof, be used for prefilling e.g. at the beginning of the braking viae.g. a pressure relief valve by conducting corresponding volume into thedriven piston circuit by way of this excess pressure through the primarycollar of the compression rod piston (driven piston). The volumerequired for applying the brake shoes thus does not have a significanteffect on the pedal stroke and possibly has an effect corresponding tohigher forces, which burden the spindle, the ball screw drive (KGT) andthe bearings.

Further reductions of the structural length are possible according tothe invention through the following measures. Shortening the pistonstroke. Proceeding from a quick switch from prestroke to return stroke,sufficient volume with adequate dynamic is normally delivered via thedouble stroke piston into the brake system. To this end, a free travelbetween pedal plunger and piston plunger corresponding to the stroke ofthe travel simulator is determined, e.g. 16 mm. Due to the free travel,so-called hydraulic free travel clearance is not required in order toavoid a collision with the piston plunger taking place in the case offull control of the pedal plunger and travel simulator. The minimumpiston stroke results from the maximum pedal stroke minus free travel,e.g. 36-16 mm=20 mm, which is sufficient for the above-mentioned volumedelivery. In the case of the motor failing, the auxiliary pistondelivers the required volume by injecting into the brake circuit in thefallback level.

A further reduction of the structural length is possible by enlargementof the floating piston and shorter stroke, whereby the same deliveryvolume is achieved.

With these embodiments or the configurations thereof, an actuationdevice, in particular for a vehicle brake, is provided, by means ofwhich sufficient fluid volume is made available for brake activation ina surprisingly simple manner.

This can take place in a very advantageous manner without notable delayin the pressure build-up with warning of the fail-safety and possibilityto diagnose the fault.

Further configurations of the invention include additional improvementoptions, in particular developed proceeding from a brake deviceaccording to DE 10 2013 111 974.3 from the applicant (to which referenceis hereby made).

Travel simulator (WS) systems are connected with a fixed pedal forcetravel characteristic as is well known. The driver of present brakesystems with ABS is, however, used to detecting a response of thevibrating pedal and fading by a longer pedal travel in the case of low μeven with a short pedal travel.

In the context of CO₂ reduction, a low-residual friction brake should beprovided, which is possible by corresponding play. However, this resultsin a larger volume uptake and delay in the pressure build-up.

Structural length determines, amongst other things, the main cylinderpiston stroke which is included several times in the structural length.More volume should still be available in the brake circuit throughsuitable measures in the case of shorter stroke.

In particular, the following advantages can be achieved with theseadvantageous configurations:

Prefilling (VF) by controlling the AS valve using pressure signal ormotor current, of the piston stroke and the pedal speed. A lot of volumecan thus be injected into the working chamber of the compression rodpiston via the collar by way of the large effective piston area of thepiston cylinder unit, in particular of the double stroke piston even inthe case of short stroke. This advantageously takes place e.g. dependingon the pedal speed V_(P), since in the case of low V_(P) a lowerdeceleration (pressure) is generally required compared to high V_(P),which aim at full braking. In the case of low V_(P), a VF pressure of 5bar is, for example sufficient, in this regard play of the brakes isalso advantageously covered. In the case of large V_(P), a VF pressureof 30 bar is sufficient. In this connection, up to 50% more volume isgenerated with a relatively small main cylinder (HZ) stroke. The maincylinder stroke can thus be selected to be shorter, which is included inweight and structural length. Since the prefilling starts at the sametime as the beginning of the stroke movement, no collar wear occurs dueto the breather bore since, in this connection, the collar no longerslides over the breather bore of the compression rod piston. Theprefilling has a larger volume in the brake circuit as a result which,in the case of withdrawing the brake pedal, disrupts the relation ofS_(P)=f (p) via the travel simulator, in particular in the case of shortpedal strokes. In addition, this would also result in a high load on thecollar towards the end of the stroke. In order to avoid this, pressurereduction takes place in the case of large prefilling through theopening of the valve AV and volume outflow in the return flow to thereservoir (VB).

With the prefilling, a temporally quicker pressure build-up time to lockcan also be achieved. The prefilling can also be used for extreme casesof failure of the motor e.g. due to low μ. The travel simulator strokecan be fully controlled in this case and the pressure in the brakecircuit is very low. The remaining piston stroke in the fallback levelis correspondingly lower with lower volume. The prefilling can also beused here until a pressure limit is reached, which deliversapproximately 30% more volume or pressure.

In connection with the system having longer free travel and shorter maincylinder stroke, it is particularly advantageous to inject into thecompression rod piston circuit via the piston cylinder unit, inparticular double stroke piston, together with a special valvearrangement in the travel simulator with choke. This injecting (ES) isalso advantageous in the fallback level in the case of motor failure inorder to inject additional volume from the auxiliary circuit into thecompression rod piston circuit.

The diagnosis of safety-relevant functions is also important. Theseinclude, amongst others, the function of the coupling and freedom ofmovement of the piston plunger, which are used in the case of a failedmotor, if the pedal plunger directly shifts the compression rod pistonto generate pressure.

The low-residual friction brake has a high potential for CO₂ reduction.As is well known, nowadays after braking, the brake pads without freemovement generate additional friction which corresponds to 2-4 g CO₂/km.This can be improved by a strong rollback or by withdrawing the brakepiston via negative pressure as is described in DE 10 2008 051 316.4 A1from the applicant.

However, the air gap resulting in this connection is a problem, whichmeans additional volume and time delay in the pressure build-up forapplying the brake pads. An advantageous solution for this is prefillingand an adaptive air gap adjustment via negative pressure. Said playadjustment no longer has an effect in the fallback levels unlikerollback for example. The additional volume for the play is thus avoidedsuch that a higher pressure level and improved pedal characteristicresults.

Furthermore, in the case of the system with multiplex arrangement oroperation (MUX), there is simultaneously P_(auf) via return stroke in abrake circuit (BK) and P_(ab) in the other BK by corresponding pistonmovement.

Advantageous exemplary embodiments as well as further advantages andfeatures of the invention and the configurations thereof are depicted inthe drawing and described in more detail below.

DESCRIPTION OF THE FIGURES

They show:

FIG. 1 a brake system with the double stroke piston according to theinvention;

FIG. 2 a section of the brake system with double stroke piston withvalve connection;

FIG. 3 a section of the brake system with an alternative valveconnection;

FIG. 4 a depiction of the double stroke piston;

FIG. 5 the temporal volume delivery in three stages;

FIG. 5a a summary concerning stage 1;

FIG. 5b a summary concerning stages 1 and 2;

FIG. 6 a different embodiment of a brake system with a double strokepiston according to the invention;

FIG. 6a an embodiment with idle stroke and injection from an auxiliarypiston, wherein in the upper half of the figure the spindle of the driveis connected to the piston by means of a connection element, inparticular a bending rod and by means of a coupling in the lower half;

FIG. 7 an embodiment with a device for avoiding the escape of leakagefluid to the outside;

FIG. 8 an alternative valve connection of the double stroke piston;

FIG. 9 a double stroke piston with an expansion for prefilling the brakecircuits;

FIG. 9a a double shutoff valve;

FIG. 10 an embodiment with an annular piston;

FIG. 10a a double seal on the double stroke piston configured as anannular piston;

FIG. 10b a structural separation of annular piston and driven piston;

FIG. 11 the arrangement according to FIG. 1 with double stroke pistonand floating piston in parallel or twin arrangement;

FIG. 12 the piston cylinder unit (THZ) with auxiliary piston and theactuator with double stroke piston as parallel system;

FIG. 13 another embodiment of the double stroke piston;

FIG. 13a an expansion of the embodiment depicted in FIG. 13 with adifferential piston;

FIG. 14 a further embodiment with parallel piston capable of returnstroke;

FIG. 15 an entire system with structuring of the functional blocks;

FIG. 15a an adaptive travel simulator (WS);

FIG. 16 Valve connections; and

FIG. 17 an auxiliary piston in block B.

The brake system depicted in FIG. 1 is based, for example on the brakesystem depicted and described in DE 10 2013 105377 from the applicant towhich reference is hereby made also for purposes of disclosure.

The brake system substantially consists of an actuation device, inparticular a brake pedal 1, a pedal interface 14 with an auxiliarypiston 16 and redundant pedal stroke sensors 2, a drive with a motor 8and transmission, in particular a ball screw transmission 7 with aspindle 5, a piston cylinder unit actuatable by means of the drive, inparticular the spindle 5, a tandem main cylinder (THZ) 13 with adirectly driven double stroke piston 10, which rests on the spindle 5and a directly, i.e. hydraulically driven floating piston 12. The doublestroke piston 10 is configured in a stepped manner and forms an annularspace 10 a by means of the stepping. Between the drive, in particularthe spindle 5 and the double stroke piston 10, a coupling 9 is arranged,which acts mechanically in this case and is mechanically actuatable. Anexample of a coupling of this type is described in EP 2217478A2 from theapplicant to which reference is hereby made and is thus onlyschematically depicted in FIG. 1. A reservoir 11 is connected to thepiston cylinder unit 13 via hydraulic lines and with the pressurechambers 10 b, 12 b of the piston cylinder unit 13 and via a normallyopen solenoid valve AS with the annular space 10 a. The annular space 10a is also connected to the brake circuits A, B via hydraulic lines, inwhich the normally closed solenoid valves EA are connected. Furthermore,a travel simulator device WS and further valve device described indetail below as well as an electronic control or regulating device (ECU)(not depicted) are provided.

The brake pedal 1 acts on the auxiliary piston 16 arranged in the pedalinterface 14. Said auxiliary piston acts on the pedal plunger 3 and thelatter acts on the piston plunger 4. The pedal plunger 3 and the pistonplunger 4 can be separated or connected to each other. An idle stroke orfree travel LW is provided between the pedal plunger 3 and the doublestroke piston 10. In the case of the example depicted in FIG. 1, thefree travel LW is provided between the end of the piston plunger 4 andthe coupling 9. In the case of the embodiment according to FIG. 6, thefree travel LW is provided between the separately configured pedalplunger and the piston plunger. If long free travel corresponding to DE10 2013 105377 from the applicant is not provided, in the case of thealternative with short free travel the free travel between pistonplunger 4 and coupling is approximately zero, the coupling is thus movedwith each braking. This has the advantage that a jam can be diagnosed.

The piston plunger 4 acts via the coupling 9 on the double stroke piston10, which is configured in particular in a stepped manner and forms anannular space 10 a. This annular space 10 a is connected to thereservoir 11 and the brake circuits A, B via hydraulic lines.

The motor 8 is normally controlled via the pedal stroke sensors 2 andacts via the rotor, ball screw drive (KGT) 7 and the spindle 5 by way ofa short play on the piston 10. This generates pressure in the brakecircuit A, which acts via the floating piston 12 in the brake circuit Bin a manner known per se. Preferably, the pistons are arranged in atandem main cylinder (THZ) 13. Twin arrangements are also possible inthe context of the invention.

Below, the pressure build-up P_(auf) and pressure reduction P_(ab) arefirstly described for the normal brake function, then for the ABSfunction. The function of the travel simulator device WS is described inDE 10 2013 105377 from the applicant to which reference is hereby made.

In the case of the function of the pressure build-up P_(auf), the doublestroke piston 10 and floating piston 12 come into the region of thestroke end, which is detected in the double stroke piston by the motorsensor 6 via the rotor revolution and spindle pitch (stroke). Themovement (position) of the floating piston 12 can be assessed from thespindle stroke and the pressure determined by a pressure sensor DGprovided in the brake circuit A using the known assessment of thepressure-volume characteristic curve. If the stroke end is now reached,the motor 8 and the spindle 5 are switched from prestroke to returnstroke. In this connection, the normally open valve AS arranged inhydraulic line to the reservoir 11 is closed and one or both of thenormally closed valves EA arranged in hydraulic lines to the brakecircuits A, B is open. The spindle 5 now moves the double stroke piston10 back via the closed coupling 9 and the volume from the annular pistonspace 10 a now reaches into the brake circuits A and B via the EA. Thiscan take place simultaneously or serially. If the end of the returnstroke is now reached, then the prestroke takes place again with theclosing of the valves EA and opening of the valve AS.

The return stroke depends, in this regard, on the position of the pedal1 or the pedal plunger. In the case of full control of the travelsimulator WS, the return stroke can be approximately 60% of theprestroke, which, however, delivers sufficient volume. In the case of anormal vehicle, the return stroke is required only in the fading region,in the case of small commercial vehicles it can even take place with 50%braking.

Borderline cases are conceivable, in which the additional volumedelivery via the return stroke starts earlier, e.g. in the case of asmall leakage or vapour bubble formation. It is advantageous in thismethod for the volume delivery to be able to take place in a highlydynamic manner and without notable time delay theoretically only limitedby the supply in the reservoir 11. This in the case of relatively smallpiston dimensions and corresponding spindle forces.

Valve Connections:

The ABS regulation can take place in the preferred and often describedmanner by valves SV in the multiplex (MUX) method, wherein only onevalve SV is in each case provided per wheel brake RZ (not depicted), asthis is depicted in FIG. 1 for the brake circuit A. By way of thepossibility of continuous volume delivery, the conventional method ofpressure control can also take place via inlet valves E and outletvalves A (one valve E and A each per wheel brake RZ), as this isdepicted in FIG. 1 with regard to the brake circuit B. The volumerequired for the pressure reduction P_(ab) which is conveyed via thereturn flow line R into the reservoir, can be supplemented by the volumedelivery of the piston 10.

The E or A valves still have additional functions. In the case ofregulation due to low μ, the piston 10 must be moved very far back,which would lead to a collision with the pedal/piston plunger. In orderto avoid this, an opening of the EA valve and pressure reduction fromthe brake circuit can expediently take place, as this is described in DE10 2010 045617 from the applicant (so-called HLF). The volume from thebrake circuit A or additionally B can be conveyed for the pressurereduction into the reservoir 11 via the piston 10 or the associatedpressure chamber and the valve AS.

Alternatively, a free travel LW can be provided between pedal and pistonplunger, as is described in detail e.g. in DE 10 2013 105377 from theapplicant. A further borderline case is conceivable by locked motor orspindle. The vehicle remains braked in this case. In this connection,the pressure can be released via the E/A valves.

In the fallback level (RFE), the coupling between the spindle 5 and thepiston 10 is expediently separated, i.e. the coupling is open, sinceotherwise the RFE effect is reduced by the additional force to overcomeresidual torque and spindle return spring, which accounts forapproximately 15% such that the 0.64 g cannot be reached. The pistonplunger thus separates the coupling 9 in the RFE and acts directly onthe double stroke piston 10. If, e.g. for reasons of cost the couplingis left out, a corresponding reduction of the efficiency results. It isalso conceivable to make the piston of the piston cylinder unit (THZ) 13smaller in diameter since the quick supply allows this and sufficientpressure medium volume is provided in the fallback level via injecting.

In order to improve the pedal travel in the fallback level, as describedin DE 10 2013 105377 from the applicant, volume from the pressurechamber of the auxiliary piston 16 can be conveyed via the valve ESVinto the brake circuits. This can take place in this case e.g. via thevalve ESV into the brake circuit A. Alternatively, pressure medium canbe conveyed via the valve ESV on the rear side of the piston 10(corresponding to the line marked in a dashed manner in FIG. 6). Thishas the advantage that a brake circuit failure does not occur in thecase of a leakage of the valve ESV. In addition, depending on theposition of the pistons 10, 12, pressure medium volume can also beinjected via the valves EA into the brake circuits. This injecting isparticularly advantageous for a solution with idle stroke, as isdescribed in DE 10 2013 105377 from the applicant. The impinging of thepedal plunger on the double stroke piston 10 can be detected via thepedal travel sensor 2.

FIG. 2 shows an additional, normally closed safety valve SiV in the linefrom the annular space 10 a of the double stroke piston 10 to the valvesEA. Unsealed EA valves result in a brake circuit failure since theleakage volume reaches into the reservoir 11 via the double strokepiston 10. This impedes the redundant SiV in the line to the reservoir11 via the valve AS. The valve AS can also be configured redundantly byparallel connection of a second valve. It is thus ensured that apressure build-up is possible even in the case of a valve failing.

FIG. 3 shows a simplified valve connection for the control of the doublestroke piston 10. Instead of the valves EA and AS, a 3/2 way solenoidvalve MV can be used for each brake circuit A, B, which saves the valveAS because the annular space 10 a of the valve 10 is connected via the3/2 solenoid valve to the reservoir in the outlet position. In theconnected state, this connection is closed and the annular space 10 a isconnected to the brake circuit A or B via the 3/2 solenoid valve. Thisis only depicted for a brake circuit A in the figure since analternative embodiment is shown for the others. One 3/2 solenoid valvewould then also be used for the brake circuit B. An SiV (not shown) canalso still be used here in addition in the line. For brake circuit B,the opening of the brake circuit B can be avoided by a plunger 17together with the EA valve.

FIG. 4 shows the stepped double stroke piston 10 with the annular space10 a and the different effective areas A1-A3 thereof in an enlargedmanner. The volume for the prestroke is determined from volumeV_(V)=A₁×piston stroke, the following applies for return strokeV_(R)=(A₂−A₃−A₁)×piston stroke. Preferably, V_(R) is selected so as tobe smaller, a smaller piston force=motor torque is thus required for thehigher pressure range if only one return stroke is required.

In the case of two prestrokes, the same effect can optionally beachieved by one idle stroke for the prestroke by the prestrokedelivering into the reservoir 11 in the case of a closed valve SV.

FIG. 5 shows the temporal volume delivery in three stages via thetwo-fold prestroke VH and one return stroke RH. The switch time fromprestroke VH to return stroke RH requires one only very small time delayof <10 ms.

FIG. 5a shows only one stage, which is used in the case of over 90% ofbraking operations. This phase can also be used for diagnosing theleak-tightness of the valves EA and AS. A leak from EA can be determinedby two methods. Firstly by comparing pressure and piston travel andassessing the pressure-volume characteristic curve. In the case of aleak, the known association of pressure and volume (or piston travel)would be disrupted. Secondly, the pressure can be maintained bycorresponding piston position in the case of pressure reduction P_(ab)for x and assessed via t_(D). In the case of both tests, all leakagesare detected in the brake circuits. When the SiV according to FIG. 2 isused, the valves EA can be tested separately by closing SiV.

FIG. 5b shows the volume delivery in two stages. When the brake pedalfrom stage 2 is withdrawn, the corresponding pressure is reduced byopening the valve EA, controlled via the pressure sensor DG. The DHKpiston 10 or floating piston 12 is thus prevented from moving with toomuch pressure over the breather bore in the main cylinder. The pressureis only reduced so much such that in stage 1 the normal association ofpressure to piston travel occurs, such that optionally only low pressureis used to move over the collar.

With the double stroke piston and the control possibilities described, aquick and continuous volume change is possible with relatively littleeffort which increases the application and acceptance of the system andis at the same time fail-safe.

In FIG. 6, a different embodiment of the brake system according to theinvention is depicted with a magnetic coupling 9 a and a free travel LWbetween pedal plunger 3 and piston plunger 4, which corresponds to thecontrol path of the travel simulator. In the case of this embodiment,the volume supply takes place with a modified valve connection. In thisconnection, in the case of the return stroke delivery is not carried outinto the brake circuit via fully or partially opened valves SV or valvesE, but rather into the pressure chambers 10 b, 12 b of the pistoncylinder unit (THZ) 13. In this regard, all valves SV and E are closed.It is advantageous here to use a simple magnetic coupling, as isdescribed in DE 10 2010 044754 from the applicant to which reference ishereby made also for the purposes of disclosure. This is possible withthis embodiment because a comparatively low piston force is sufficientto deliver the fluid volume from the annular space 10 a of the doublestroke piston 10 via the valves EA into the working chambers of the maincylinder which are associated with the brake circuits A, B. In thisconnection, the delivery volume of the return delivery must match theuptake volume of the main cylinder circuits by correspondingdimensioning. The valve switch position in the case of the return strokeend is depicted in FIG. 6, i.e. valve EA open and valve SV or valve E tothe wheel brake cylinder are closed. Furthermore, lower bearing forcesin the drive result in the case of the return stroke. However, thisembodiment can lead to a small time delay in the case of pressurebuild-up compared with the suction via negative pressure. Otherwise thevalve connection according to FIG. 2 and the 3/2 way valve according toFIG. 3 can be used for this embodiment.

FIG. 6a shows an embodiment similar to FIG. 6 wherein in the upper halfof the figure, the spindle of the drive is connected to the piston bymeans of a connection element, in particular a bending rod and in thelower half by means of an, in particular mechanical coupling. UnlikeFIG. 6, the volume of the auxiliary piston 16 here is, however, notdirected to the rear side of the double stroke piston 10, but rather isdirected in the fallback level RFE in the case of the vehicle electricalsystem or the ECU failing via a normally open valve ESV, with a normallyclosed valve WA, into the brake circuit. Since the breather bore at 40of the compression rod piston circuit is open in the outlet position ofthe double stroke piston 10, a shutoff valve AV to the reservoir 11 isused, which is closed at the beginning of braking. Thus no volume canflow into the reservoir 11 in the fallback level. The shutoff valve AVcan be economised if the motor is driven back against the stop springprior to the beginning of braking in order to open the breather bore.The situation in which the breather bore is closed persists even in thecase of greater pressures or pedal travels such that in the case of thepedal plunger 3 impinging on the piston plunger 4, both surfaces of theauxiliary piston 16 and of the driven piston 10 deliver volume. In thiscase a higher pedal force results, which is comparable with conventionalsystems. However, if the ECU is intact, then the injection iscontrolled, as described via ESV and WA, until a certain pressure isreached. The volume uptake of the travel simulator WS is disruptedsomewhat in the fallback level by the initially flatter course of thepedal force via the pedal travel. This can be eliminated by anadditional normally closed shutoff valve WSA.

This solution provides an additional possibility for structural lengthreduction by the stroke of the double stroke piston DHK 10 being equalto the difference of pedal stroke and free travel, e.g. 36 mm−16 mm=20mm, corresponding to the control travel of the travel simulator WS,which means a structural length reduction of 48 mm. This is possiblesince pressure is continuously built up via the double stroke piston 10.The spindle length is thus also reduced and the expensive bore in thespindle 5 can be dispensed with. In this connection, the spindle can beconnected to the double stroke piston DHK 10 via a bending rod (asdepicted in FIG. 12). However, in this case the spindle with motor hasto be moved in the fallback level RFE, which requires approximately 5%more power if the pedal plunger impinges the rear side of the spindle.Alternatively, the mechanical coupling 9 from FIG. 1 can also be used.The above-mentioned additional force is thus not required in thefallback level RFE with ECU function in the case of the motor failing. Afurther possibility of the structural length reduction is a greaterdiameter and shorter stroke of the floating piston 12. This applies forall solutions.

FIG. 7 shows an embodiment with a means for preventing the escape ofleakage fluid to the outside. Seals in hydraulic systems tend to leakunder unfavourable conditions. Double seals are often used which reducethe probability of leakages, but do not exclude them. However, seals ofthis type produce disadvantageous higher friction. Seals which affectthe footwell and also power units or the motor compartment are affected.As a solution, a corresponding housing, advantageously an extended motoror motor connection housing 21, 22 is used which comprises both outletchannels 25 and an uptake volume for the leakage flow. A separationchamber 23 with a sponge 24 is expediently provided in the lower regionof 22 in order to prevent sloshing of the fluid in particular in thecase of the vehicle accelerating and decelerating.

The corresponding leakage flow is detected by a level sensor 18. In thisconnection, it is also advantageous to combine the level sensor with theadjacent ECU. In this regard, sensors with high fail-safety can also beused. Alternatively, electrodes 20 can also be used which are arrangedin the lower region of the collecting vessel and are connected to theECU by means of an electrical line. With said electrodes, even verysmall fluid leakage quantities can be detected. For completeintegration, the HCU, which comprises the solenoid valves and thepressure sensors, is integrated. This means that a so-called 1-boxsolution is achieved, which comprises a full integration of allcomponents in one unit.

The embodiments according to FIGS. 8 and 9 build on those of FIG. 4 suchthat only the changes are described in the following description. Largeflow rates occur by way of the relatively large effective areas of thedouble stroke piston 10 with quick piston actuation, in the case ofwhich negative pressure cannot occur on the suction side of the piston.For this reason, suction valves S1 and S2 are arranged for both movementdirections (prestroke and return stroke). For the case that the deliveryquantities for prestroke are >return stroke, the surplus volume can bechannelled off via a screen. The prestroke speed is greater in theborderline case than the return stroke speed. The volume in theprestroke is thus directed via the suction valve S1 to the rear side ofthe double stroke piston 10; the open solenoid valve AS acts as asuction valve. In the case of the return stroke, the lower flow ratequantity is directed through the solenoid valve AS and S2 acts as asuction valve. In the case of the volume delivery in the brake circuit,e.g. driven piston 10, the solenoid valve AS is closed and the solenoidvalve EA is open, as already described.

FIG. 9 shows a slightly changed arrangement of the solenoid valve AS andthe suction valve. The volume is directed in this case through thesolenoid valve AS in the prestroke. This version shows the expansion ofthe driven piston 10 for prefilling the brake circuit in order to reducethe free travel on the pedal. In the prestroke, a pressure relief valveÜ operates, e.g. 4 bar such that corresponding volume reaches into thedriven piston circuit via the primary collar or driven piston collar 10and more volume is thus provided. Since this admission pressure is usedonly at the beginning of braking, the pressure relief valve Ü is openedvia a plunger 33 after prefilling (VF). Different control possibilitiesare conceivable in this case, e.g. that the prefilling (VF) operatesagain for the fallback level in the case of the E-motor failing at lowμ, i. e. pressure 0 in the driven piston circuit, which does not changeanything on the principle of the volume supply by the double strokepiston 10.

FIG. 9a shows a double valve arrangement with two shutoff valves AS1 andAS2 which are installed instead of the valve AS provided in FIG. 9. Theshutoff valves AS1 and AS2 are connected such that the current directionand current force act against the spring FAs. The current force is thusprevented from being greater than the spring force and the valveclosing.

FIG. 10 shows the basic structure of an actuation device with auxiliarypiston 16, spindle 5 and coupling 9, in which the driven piston and thedouble stroke piston 12 configured as an annular piston 28 are combined.The delivery chamber of the double stroke piston 28 is in thisconnection formed by an annular space 40 arranged concentrically to thepressure chamber of the driven piston, in which the annular piston 28with seal collar 28 a is arranged. The driven piston also draws in airvia the delivery chamber of the double stroke piston as depicted for 41.The valve arrangement corresponds to that of FIG. 9. The differentpossibilities of the pressure modulation via inlet valves EV and outletvalves AV or multiplex operation (MUX) via solenoid valves SV are alsodepicted here. In the first case, the solenoid valve EA can be replacedwith a simpler check valve RS since the pressure reduction, e.g. for thehydraulic free travel clearance can take place via corresponding outletvalves AV.

FIG. 10a shows the sealing of the annular piston 28 by the collar 28 awhich slides in the annular bore or annular space 40, the inner diameterof which is secured via the seal 34. A further seal 35 is required forthe rear side of the annular piston which acts as the primary seal as inthe case of the main cylinder. As in the main cylinder, an additionalsecondary seal 35 a can also be used here, wherein the sealed chamber isconnected to the reservoir 3. This arrangement can also be used in FIG.1.

FIG. 10b shows a divided embodiment of annular piston 28 and drivenpiston 31 which are connected via a securing ring 32 in a non-positivemanner. This embodiment is less tolerance-sensitive.

FIG. 11 shows an arrangement also with structural length reduction bythe piston cylinder unit being configured in a twin arrangement by usingthe floating piston 12 as the twin. The valve connection of the valvesAS, S2 and S3 and the screen 26 b is taken from FIG. 9. For the case ofa double fault of the motor and thus failure of the double stroke piston10 and brake circuit failure, pressure is no longer applied to thefloating piston 12. In the case of an intact motor, the floating piston12 would be operated via the double stroke piston 10 in the returnstroke if the brake circuit failed and the inlet valves EV in the drivenpiston circuit would be closed. In the case of a double fault, thefloating piston 12 is fed by the auxiliary piston 16 via the ESV andclosed isolation valve TV1.

FIG. 12 shows a parallel arrangement of tandem main cylinder THZ withthe pistons 12 and 12 a and pressure modulation device consisting ofmotor 8, transmission and double stroke piston 10. In this connection,the connection to the brake pedal with the pedal plunger is omitted incomparison to FIG. 1. The valve arrangement for pressure modulation andtravel simulator WS is the same as in the preceding figures. Since theconnection to the pedal plunger is no longer present here, a bending rod30 is used instead of the bending tube and coupling, so that the spindleeccentricity does not cause large transverse forces on the double strokepiston 10. The unit located parallel consisting of tandem main cylinderTHZ with the floating piston 12, driven piston 10 and auxiliary piston16 was already described in DE 10 2010 050133 from the applicant (towhich reference is hereby made in this regard) which requires the travelsimulator circuit with auxiliary piston, which is independent of thedriven piston circuit, which has significant advantages in terms offail-safety. In addition, the travel simulator WS can only be configuredin a two-stage manner, which saves costs and volume. In the first flatarea, the return spring acts as the 1st stage of the travel simulatorWS, the WA valve is open in this regard.

The travel simulator WS acts only in the second stage with progressiveincrease in force after the closing of the valve WA. In comparison to DE10 2010 050133 from the applicant, an improvement for the fallback levelis integrated here by using a changeover valve UV. This connects theauxiliary piston 16 to the rear side of the piston 12 a in a currentlessmanner. Thus in the case of the ECU or the motor failing, the freetravel LW required for e.g. recuperation does not lead to pedal failure,the volume of the auxiliary piston 16 is directed in this case to therear side of the piston 12 a. In the case of an intact ECU, the volumeof the auxiliary piston 16 can also be injected into the brake circuitvia ECU e.g. in the case of the motor failing.

The diagnosis of the travel simulator with auxiliary piston and maincylinder (THZ) can take place by pressure generation in the brakecircuits. In the case of the valve ESV opening, pressure medium canreach in the auxiliary piston circuit when the valve EA is closed. Inthe case of the normally open valve UV opening, pressure medium reachesin the elastic pressure medium chamber of the auxiliary piston 16 whichcan be measured at the piston stroke of the double stroke piston. Byusing the normally open 2/2 solenoid valve (not depicted) in the line ofthe auxiliary piston to the piston 12 and a normally closed 2/2 solenoidvalve in the line of the auxiliary piston to the valve ESV, thediagnosis can be expanded by also applying pressure medium to the pistonand it correspondingly moving.

The piston cylinder unit (THZ) is separated from the pressure supply viaisolation valves TV2, TV3 in the case of an intact motor and ECU,similar to the EHB or parallel systems as shown in DE 102010 040097. Theadvantage of the arrangement shown is the higher fail-safety andcontinuous volume delivery. The piston cylinder unit (THZ) from DE102010 040097 or DE 102011 081601 can also be combined with the pressuresupply dispensing with the fail-safety in the case of the travelsimulator.

Unlike DE 102010 040097, there is no pressure sensor used here since themost important parameters for diagnosis and function can be detected bymotor current and piston travel.

In order to reduce the structural length, the (twin) solution accordingto FIG. 11 can also be used here.

FIG. 13 shows, proceeding from the depiction according to FIG. 6a ,another embodiment of the double stroke piston 10. The double strokepiston 10 is neither stepped nor configured as an annular piston, butrather it corresponds in structure and sealing with primary andsecondary collar to a conventional compression rod piston. In this case,it is coupled to the spindle 5 via the piston plunger 4. A free travelLW is integrated therein, as in the case of the embodiment according toFIG. 6a . The rear side of the double stroke piston 10 is connected viaa shutoff valve AS to the reservoir (VB) 11. If further volume is nowrequired, the return stroke of the double stroke piston 10 then takesplace in the case of the closed valve AS and at the same time theisolation valves TV2 and TV3 to the piston cylinder unit (tandem maincylinder THZ) are closed. In the case of the return stroke, volume isdelivered via the check valve RS and the valve EA or alternatively viatwo valves EA into the brake circuits. At the same time, volume from thereservoir 11 is suctioned via suction valves S1 and S2 installed in thehydraulic lines leading to the reservoir 11 by the floating pistons 12or 12 b and the double stroke piston 10, said reservoir being availablefor further pressure build-up in the case of the next prestroke. Anadvantage of this construction consists of the shorter structural lengthand a simpler double stroke piston 10, which is, however, connected tomore valves.

The solution according to FIG. 13a builds on an arrangement as isdescribed e.g. in the PCT/EP 2007/009683 from the applicant and isexpanded with a double stroke piston. The inner piston 10 herecorresponds to the driven piston with breather bore 40 and the outerdifferential piston 38 corresponds to the double stroke piston. Thedriven piston is, as usual, sealed by means of primary collar andsecondary collar 27 and the differential piston via the seals 39, 35 and34 a. The valve connection of the double stroke piston with valve AS,valve RS etc. corresponds to that depicted in FIG. 13, supplemented by asuction valve (S2). This is required in order to suction the volume inthe case of the closed valve AS back into the piston after the returnstroke with volume delivery in the case of the subsequent prestroke. Thearrangement has connection lines to the reservoir VB. The differentialpiston is connected to the ball screw transmission 7 via the spindle 7and the driven piston is connected to the pedal plunger via the pistonplunger 4. Since the spindle 5 acts on the differential piston forpressure modulation and the driven piston acts only in the fallbacklevel, a coupling is no longer required. This solution can be combinedwith integrated free travel or with hydraulic free travel clearance viaat least one inlet/outlet valve EA.

A further advantageous embodiment is depicted in FIG. 14. In thisembodiment, in particular two parallel pistons are arranged parallel tothe piston cylinder unit (THZ), which are fixedly connected to thespindle. The return stroke of the spindle thus acts directly on thesepistons for volume delivery. In this connection, a valve arrangementaccording to FIG. 9 or also FIG. 13 can be used. With this embodiment,which can also be operated in the multiplex method, the volume currentscan be reduced, amongst other things, in the case of short structurallength.

Reference is then made to FIGS. 15 to 17. The entire structure of theembodiment depicted in FIG. 15 largely corresponds to the embodimentdepicted in the preceding figures and is structured in functional blocksfor better understanding.

-   -   A Motor with spindle drive    -   B Piston cylinder unit, in particular double stroke piston 10        and main cylinder piston    -   C Auxiliary piston with travel simulator (WS)    -   D Valve connection        -   D1 for pressure regulation        -   D2 for control of double stroke piston 10, prefilling (VF)            and pressure supply of main cylinder in the case of return            stroke        -   D3 Control of travel simulator (WS) with injection (ES)

A drive with a motor 8 with a ball screw drive (KGT) 7 and spindle 5 isarranged in block A which acts on a coupling 9 and a piston cylinderdevice, in particular with a double stroke piston 10. The coupling 9 isopened in the outlet position by a main cylinder return spring 123acting via a coupling return spring 122 on a piston plunger 4displaceably mounted in the spindle, said piston plunger being connectedto a coupling plunger (KS). The piston plunger 4 then rests on a stop121. If the motor 8 and the spindle 5, which acts on the double strokepiston 10, move, then the coupling 9 closes after a short coupling pathand the spindle 5 is then coupled in both directions with the doublestroke piston 10, which is required for the return stroke so that, asdescribed, the double stroke piston (which can be configured as anannular piston) delivers volume into the brake circuits of compressionrod piston 12 a and floating piston 12 via EA valves. This coupling pathhas the advantage that the plunger is moved in the case of each braking.In the case of a jam, the piston does not return into the outletposition and can be diagnosed via residual pressure in the workingchamber of the compression rod piston 12 a and a motor sensor 6.

If the motor drive fails, a pedal plunger 3 acts on the piston plunger 4after the free travel (LW) and thus on the compression rod piston 12 a,which is integrated in the double stroke piston 10. In this case, volumeis injected during the free travel from an auxiliary piston 116 via anormally open solenoid valve ESV and a solenoid valve AS and an openbreather bore 120 directly into the compression rod brake circuit. Thefree travel is thus not received as loss of travel in the volume balanceof the compression rod piston 10. This is possible by dynamic pressureoccurring by way of the floating piston 12 and a choke D (screen) to atravel simulator WS, which enables an injection of pressure medium. Inorder for further optimisation, a normally closed shutoff valve 124 canbe used together with a pressure relief valve ÜD.

In a special case, if the drive (motor/transmission) is locked and thusalso the two pistons 12 a, 12, pressure can also be built up or reducedfrom an auxiliary piston 116 via the valves EA.

After bridging the free travel, the pedal plunger 3 impinges on thepiston plunger 4 and in the subsequent movement overcomes the force jumpwhich results through the main cylinder return spring 23 and thepressure generated by the compression rod piston 12 a. Thespeed-dependent dynamic pressure acts on the auxiliary piston 16 in thisconnection as a hydrodynamic force on the choke D. In the case of theforce jump, the speed briefly becomes low, such that the pressure on thecompression rod piston 12 a does not fully add up to the dynamicpressure prior to impinging=dynamic pressure.

A small additional force jump thus occurs. The jump force can be definedby an elastic stop 21 with a transition function. This force jump isbased on the pedal force prescribed by the legislator of 500 N forminimum braking in the fallback level in the range <10%, thuscontrollable by the driver. This jump force applies for the fallbacklevel (RFE 3, i.e. failure of motor and vehicle electrical system). Inthe case of motor failure and intact ECU (=RFE 2), the auxiliary pistonpressure in this range can be controlled by pulse width modulation (PWM)of the solenoid valve (ESV) and the solenoid valve (WA).

If, depending on the valve connection, even in the case of longer travelof the auxiliary piston 16, dynamic pressure has an effect whichrequires a higher pedal force which reduces the maximum pressure at e.g.500 N pedal force, then a bypass can be used here in the auxiliarypiston bore. This causes an outflow of fluid in the return flow with thecorresponding piston position. Without this feature, a return flow fromthe auxiliary piston to the reservoir (VB) 11 is not required.

Unlike the embodiments described in the patent applications DE 10 2010045 617.9 A1 and DE 10 2013 111 974.3 from the applicant, the valve ESVis, in addition to the valve WA, normally open, which enables theinjection in the fallback level without significant disadvantages. Thusthe variant with free travel and reduced main cylinder stroke ispossible, which leads to notable structural length reduction and costreduction. The lower delivery volume of the main cylinder with reducedstroke is balanced out by prefilling, as will be explained below in moredetail.

The function of the travel simulator (WS) with the valves ESV, WA, RV0,RV1, D are described further in the patent applications DE 10 2010 045617.9 A1 and DE 10 2013 111 974.3 from the applicant to which referenceis hereby made in this respect.

The piston cylinder device with the main cylinder piston 12 and 12 a andthe double stroke piston 10 are contained in block B and the valvefunctions for ABS/ESP and pressure supply with control of the doublestroke piston 10 are parallel.

The injection via the breather bore 120 was already described furtherabove which substantially only applies for the fallback level (RFE). Inthe case of an intact motor, pedal travel sensors 2 a and 2 b deliver asignal to the motor control for the pressure build-up even after shortpedal plunger travel. In this regard, the prefilling immediately comesinto operation by closing the AS valve. In this connection, the fulldouble stroke piston delivers a large volume from the area of theannular space 10 a and the compression rod piston 12 a even in the caseof short travel which is used for prefilling. In this connection, anadditional effect occurs by the prefilling volume flowing through thecollar of the compression rod piston 12 a and preventing it from beingworn out by the breather bore. The prefilling should be e.g.speed-dependent, in the case of stage 1 small V a low pressure <10 barand stage 2 high V<40 bar. In this connection, the measured pressure ofthe pressure sensor D6 or the current or the piston position can be usedas the control signal. In the case of the special design of the doublestroke piston with two pistons in particular with an annular piston,both the prefilling and the additional volume delivery can be carriedout in the return stroke via only one valve (AS). In the case of otherdesigns of the double stroke piston, two or a plurality of valves can ormust be used for the prefilling.

The prefilling has two important advantages:

-   a. In the case of short brake pad—play, i.e. additional volume    requirement, the pressure build-up so-called time to lock is faster    which means brake travel reduction.-   b. In the case of play LS, e.g. with rollback, the additional volume    is not notably included in time to lock. In this connection, the    brake pad play control described in the patent application DE 10    2008 051316.4 from the applicant to which reference is made here in    this respect lends itself to the play control by controlling the    negative pressure in the brake piston. In this connection, the play    can be variably designed e.g. vehicle speed-dependent or dependent    on the RFE. This play is a significant contribution to CO₂ reduction    in the range of 1-2 g.-   c. In the case of a large volume requirement in the main cylinder    for full braking and great pedal speed, 50% greater volume is    generated in the case of <40 with the same HZ stroke. The    advantageous variant with free travel (LW) and shorter main cylinder    travel is thus justified.-   d. In the fallback level RFE1 (with failure of the travel    simulator), a switch is carried out to a so-called slave booster    because the pedal plunger here acts on the HZ piston in the case of    the conventional brake force booster (BKV).

Since however in order to achieve greater pressures at 500 N of pedalforce, as is well known, a small main cylinder diameter is used, thepedal travel without travel simulator WS is correspondinglysignificantly longer. This can be reduced by approximately 30% withprefilling. The greater prefilling volume can influence the pistonposition such that the floating piston 12 is possibly at the stop at anearly stage. This can be prevented by the floating piston 12 being givena larger diameter. Otherwise, the stop is detected by pressure=f (pistontravel), measured by the motor sensor. In the case of the stop, thereturn stroke volume (i.e. the volume that is delivered in the case ofthe return stroke) is injected into the brake circuit of the floatingpiston. The association of the pistons can also be detected via afloating circuit piston travel sensor 15 with target 15 a in the piston.

In particular in the case of systems with recuperation, a pedal freetravel between pedal plunger and the piston of the piston cylinderdevice, in particular double stroke piston 10 is advantageous, since dueto the brake torque of the generator pressure does not have to be builtup by the piston cylinder device. The brake torque is predetermined by apedal travel sensor together with the travel simulator and divided intogenerator brake torque and brake torque corresponding to the pressure.If e.g. a small brake torque is predetermined by the driver, thegenerator brake torque is then sufficient. This applies up to a braketorque of approximately 30 bar which can be applied by the generator.The pedal travel range of approximately 5-8 mm corresponds to the freetravel. The travel of the piston 10 of the piston cylinder devicebecomes shorter by this free travel since the pedal stroke ispredetermined and a short stroke of the piston 10 results after the freestroke. In the fallback level, this stroke is omitted in the case of theentire volume delivery of the piston 10. According to the invention,volume from the auxiliary piston 116 is thus injected via the piston 10and the open breather bore of the compression rod piston into thecompression rod piston brake circuit.

The prefilling with greater volume must, however, be taken intoconsideration in the case of the pressure reduction since based on thepedal travel range, in particular in stage 1 of the travel simulator WS,the travel simulator piston still does not operate (see Description FIG.1a ). A pressure reduction P_(ab) takes place here depending on thepedal travel reduction in the reservoir 11 via the outlet valves, as inthe case of ABS. In order to control the double stroke piston 10, thevalve AS and suction valves S2 and optionally S3 to the reservoir arerequired. S2 operates in the case of closed valve AS in the case of thereturn stroke and volume delivery via EA into the brake circuit. S3 isoptionally required since in the case of prefilling, the valve AS isclosed and what occurs here in the case of negative pressure cannot bebalanced out as quickly after prefilling in the case of a re-openedvalve AS.

In the case of the return stroke, a smaller spindle force and also motortorque operate in the case of corresponding dimensioning of the doublestroke piston 10, which is advantageous in the case of high pressures.This phase can also be correspondingly designed by being used as avirtually free run in the case of applied prestroke for the highpressure range such that volume does not reach the pressure build-upP_(auf), but rather reaches the reservoir 11 in the return flow. Volumefor the high pressure range is then delivered only in the case of thesubsequent return stroke.

The return stroke in the case of advantageous system variants withmultiplex arrangement or operation (MUX in which the pressure build-upand the pressure reduction takes place in each case via only one valvein the brake lines) can take place during simultaneous pressure build-upP_(auf) and pressure reduction P_(ab) in separated brake circuits. Tothis end, an additional shutoff valve 17 is required.

The valves for ABS/ESR pressure control are located in block D1, whichwere described e.g. in the patent application DE 10 2013 111974.3 fromthe applicant to which reference is made here in this respect. In thecase of conventional pressure control with inlet valves (EV) and outletvalves (AV), the pressure reduction P_(ab) takes place through theoutlet valves (AV) in the return flow to the reservoir 11.

The valve function of the valves AS and EA was already described inblock D2. In the patent application DE 10 2013 111974.3 from theapplicant, only one check valve is used instead of the valve EA. This isdisadvantageous e.g. in the case of brake circuit failure, e.g. of thefloating piston brake circuit, where supply by return stroke is notpossible, since the return stroke volume is possibly delivered in thepressureless floating piston circuit. Since this is detected bydiagnosis p=f (piston travel), no delivery takes place into the failedcircuit in this case with the EA valve.

In the embodiment with MUX, the valves for pressure regulation have noreturn flow. For the case described of larger prefilling volume andpressure reduction P_(ab) to balance out with shorter pedal travels, avalve AV_(x) for pressure reduction P_(ab) must be used here.

Block C contains the pedal interface with auxiliary piston 116, pedaltravel sensors 2 a and 2 b and travel simulator WS. The functions arealready described in previous applications from the applicant and alsoapply to the system design with double stroke pistons. The valvefunctions of block D3 were described in connection with injection ES.The diagnosis of the breather bore 120 in the compression rod piston 12a should also be mentioned which is not always possible withconventional brake systems. This case occurs by way of tolerance shiftsor disruptions during operation. If the breather bore remains closed,pressure balance in the brake circuit is not possible. This results in anegative pressure in the case of lower temperatures with possible playif the brake piston reacts to this or in the case of high temperature aresidual pressure in the brake circuit leads to a residual brake effectwith possible temperature increase in the brake.

In the case of the proposed system with prefilling, a residual pressurein the compression rod piston brake circuit still remains in the rangeof the free travel LW which can be controlled via the valves AV and ESV.In this case, valve ESV is closed and valve EA is open; differentialpressure does not thereby occur on the collar since the pressure in thebrake circuit of the compression rod piston and double stroke pistonbrake circuit is equal. In the case of pedal travel=0 (i.e. outletposition), the valve EA is closed and the valve ESV is open. Thefollowing pressure change is an indication that the breather bore isopen. This method can be used for each braking or at large intervals.

FIG. 15a shows the adaptive behaviour of the travel simulator WS. Thetravel simulator WS has at least three stages in terms of itscharacteristics:

-   Stage 1: Pedal return effect is generated via the pedal return    spring 118. Valve WA open. This stage is dimensioned e.g. with 7-8    mm pedal plunger travel and towards the end results in a system    pressure of approximately 30 bar. This pressure corresponds    approximately to the braking with a high recuperation torque of the    generator. The described free travel LW of the pedal plunger    corresponds to approximately the previously mentioned travel which    means that in the case of recuperation the actuator with motor drive    is not enabled which requires approximately 80% fewer load cycles.-   Stages 2 and 3: Valve WA closed, volume of the auxiliary piston 16    reaches in the travel simulator piston with specific force-pressure    characteristics with stop.

In the case of known systems, the stop of the travel simulator isassociated with a fixed pedal travel via a valve WA. According to anadvantageous inventive aspect, a solution is now proposed, in which thetravel simulator is adaptive e.g. in the case of fading which isdetectable due to the function p=f (vehicle deceleration). The stop isnormally reached in the case of N. In the case of fading which isdetectable by high pressure in relation to the vehicle deceleration, thestop can be shifted to F by control of the valve WA. In the case of lowp, this is also detected and the stop can be provided in the case ofshorter pedal travels. As is well known, the conventional ABS operateseven in the case of shorter pedal travels E1. This can also be generatedby the pressure reaching in the auxiliary piston via open valves EA andESV through prestroke and pushes back or modulates the latter or viaclosed valve EA and open valve ESV with return stroke.

FIG. 16 shows simplified valve connections without details of theregions A-C. In the region D2, only one 3/2 way EA valve with checkvalve is used for the pressure supply of the brake circuits. The volumeis delivered in the floating circuit without connecting the valve EA inthe case of the return stroke of the double stroke piston. In the caseof connecting the EA valve, delivery takes place in the floating pistonbrake circuit and the brake circuit of the compression rod piston. Inthe case of failure in the floating piston brake circuit, delivery isonly carried out in the floating piston brake circuit. The compressionrod circuit also has the advantage with the double stroke piston that afailure of the collar is very quickly detected by the pressure andpiston travel monitor. In this case, delivery is nonetheless carried outin the compression rod brake circuit with closed valve ESV. In thisconnection, the driven piston pressure is balance out with open valveAS.

A further simplification is possible in the case of the travel simulatorWS. The normally open valve ESU is replaced with a check valve RVS. Thissolution has the disadvantage of the travel simulator pressure beingshifted in the double stroke piston and causing additional sealfriction. In an extreme case, the WS pressure may become greater thanthe pressure in the compression rod piston brake circuit in the case ofvery high pedal forces. In this case, the ABS function must be switchedoff. This can be avoided if the piston movement of the travel simulatorWS (see dashed line) is expanded for additional closure of the checkvalve. In the case of this simplification, pedal reaction cannot begenerated in the case of the adaptive travel simulator.

FIG. 17 shows a constructive variant by the auxiliary piston beingshifted from the pedal interface in block B. In this connection, thepedal plunger 3 acts on the annular auxiliary piston 119 via a bridge,said auxiliary piston being mounted between double stroke piston 10 andthe housing 125 thereof. The pedal stroke 3 also acts on the coupling 9.The pedal return spring 18 acts on the auxiliary piston 119 analogouslyto FIG. 15. The movement of the auxiliary piston 19 can alternatively bedetected here at another point by the slave pedal travel sensor 2 b. Theadvantage is the overview of all hydraulic functions in one blockwithout long supply lines to the pedal interface corresponding to FIG.15.

For future vehicle platform modularity, the systems should be able to beused via numerous models for left-hand drive vehicles and also forright-hand drive vehicles. In this regard, the right-hand drive vehiclehas problems in the case of the transverse mounting of the combustionmotor. A 2-box solution lends itself in this situation by only the maincylinder with small dimensions, in particular tandem main cylinder withauxiliary piston (16) being mounted on the bulkhead of the vehicle andthe drive (or motor/transmission) valve module flexibly in the motorcompartment of the vehicle.

LIST OF REFERENCE NUMERALS

-   1 Brake pedal-   2 Pedal travel sensors-   3 Pedal plunger-   4 Piston plunger-   5 Spindle-   6 Motor sensor-   7 KGT-   8 EC motor-   9 Coupling-   9 a Magnetic coupling-   9 b Direct coupling of spindle with double stroke piston-   10 double stroke piston-   10 a Annular space-   10 b Pressure chamber-   11 Reservoir-   12 floating piston-   12 a driven piston-   12 b floating piston enlarged-   13 Piston cylinder unit-   14 Pedal interface-   15 floating piston positioning sensor-   15 a Target for positioning sensor-   16 Auxiliary piston-   17 Plunger piston-   18 Level sensor-   19 Electrical connections to ECU-   20 Electrodes-   21 Leakage flow-   22 Housing extension-   23 Separation chamber-   24 Sponge-   25 Outlet channels-   26 Screen-   27 driven piston collar-   28 Annular piston-   28 a Annular piston seal-   29 Return spring-   30 Bending rod-   31 driven pressure piston-   32 Securing ring-   33 Plunger-   34 Seal-   35 Primary seal-   36 Secondary seal-   37 Stop spring-   38 Differential piston-   39 Differential piston seal-   40 Breather bore-   43 Working chamber-   45 Piston cylinder unit-   46 Piston cylinder unit-   115 floating piston positioning sensor-   116 Auxiliary piston-   116 a Bypass for Hiko-   117 Shutoff valve for MUX-   118 Pedal return spring-   119 Annular auxiliary piston-   120 Breather bore-   121 Stop for piston plunger (KS)-   122 Return spring for KS-   123 HZ return spring-   123 a HZ return spring-   124 Shutoff valve to WS-   125 double stroke piston housing-   WS Travel simulator connection-   AS Shutoff valve-   WA WS cut-off valve-   WSA WS shutoff valve-   ESV Injection valve-   EA Inlet/outlet valve-   SV Switch valve-   E Inlet valve-   A Outlet valve-   SiV Safety valve-   RZ Wheel cylinder-   R Return flow line-   BKV Brake force booster-   DG Pressure sensor-   RFE Fallback level-   VH Prestroke of the double stroke piston-   RH Return stroke of the double stroke piston-   T_(D) Diagnosis time-   S1 Suction valve-   S2 Suction valve-   S3 Suction valve-   Ü Pressure relief valve for prefilling (VF)-   R5 Check valve to the brake circuit-   TV1 HiKo isolation valve-   TV2 Isolation valve to the driven piston circuit-   TV3 Isolation valve to the floating piston circuit-   UV Changeover valve-   VB Reservoir-   LW Free travel

What is claimed is:
 1. An actuation device for a vehicle brake,comprising: an actuation device in the form of a brake pedal, at leastone piston cylinder unit which is connected to the vehicle brake via ahydraulic brake circuit to supply pressure medium to the brake circuitand to apply pressure on the vehicle brake, and an electromotive drivefor the piston cylinder unit, wherein the at least one piston cylinderunit includes a piston arranged to be directly driven by theelectromotive drive, wherein said piston is a double-stroke pistonarranged to supply pressure medium to the brake circuits in a controlledmanner in both movement directions of the piston, forward stroke andreturn stroke, wherein at least a first pressure chamber limited by thedriven piston supplies pressure medium at the forward stroke and atleast a second pressure chamber supplies pressure medium at the returnstroke, and wherein both pressure chambers are able to be connected by avalve device comprising at least one valve, and wherein an area of thedouble-stroke piston that is effective at the forward stroke is of adifferent size from an area that is effective at the return stroke,wherein the different effective areas are able to be used for reductionof a piston force or a motor moment by connecting the effective area atthe return stroke with the area effective at the forward stroke with atleast one solenoid valve.
 2. The actuation device according to claim 1,wherein the connection between the first and second pressure chambers bythe valve device, including the at least one valve, is a directconnection, whereby the valve device is arranged without any othervalves or other components between the first and second pressurechambers and the valve device.
 3. The actuation device according toclaim 1, wherein, by actuating the valve device, the double-strokepiston is enabled to provide a continuous pressure increase by supplyingpressure medium at the forward stroke and the return stroke.
 4. Theactuation device according to claim 1, wherein the double-stroke pistonis enabled to be used for pre-filling wheel brakes with pressure mediumat the beginning of braking by conducting corresponding volume into thebrake circuit.
 5. The actuation device according to claim 1, whereinpressure medium from a further piston-cylinder unit reaches thedouble-stroke piston by means of an auxiliary piston and a valve device.6. The actuation device according to claim 1, wherein the pistoncylinder unit forms an annular space from which the pressure medium isenabled to be supplied to at least one brake circuit.
 7. The actuationdevice according to claim 1, wherein the at least one piston cylinderunit comprises one or more pistons, and wherein the supply of thepressure medium takes place in at least one pressure chamber associatedwith the one or more pistons of the at least one piston cylinder unit.8. The actuation device according to claim 1, further comprising valvesconfigured to control supply of the pressure medium.
 9. The actuationdevice according to claim 1, wherein volume control and injection in atleast one brake circuit takes place via a return stroke of the piston.10. The actuation device according to claim 1, wherein supply of thepressure medium by means of the piston in at least two brake circuitstakes place simultaneously or serially, and wherein the actuation devicefurther comprises a closing valve.
 11. The actuation device according toclaim 1, further comprising at least one securing valve provided in asupply line for the pressure medium.
 12. The actuation device accordingto claim 1, further comprising a mechanical coupling arranged forseparating the drive and the piston driven by the drive in case of brakesystem failure.
 13. The actuation device according to claim 1, furthercomprising a positioning sensor for the driven piston and configured forcontrolling supply of the pressure medium.
 14. The actuation deviceaccording to claim 1, further comprising a reservoir configured tobalance out supplied pressure medium volume.
 15. The actuation deviceaccording to claim 1, wherein a diagnosis of valves and seals takesplace during a normal operating process.
 16. The actuation deviceaccording to claim 1, wherein pressure medium from a furtherpiston-cylinder unit reaches the double-stroke piston by means of anauxiliary piston and via a valve.
 17. A double-stroke piston for ahydraulic actuation device, wherein the double stroke piston isconfigured according to claim
 1. 18. The actuation device according toclaim 1, further comprising a housing extension provided on a drivehousing, said housing extension forming at least one outlet channel forleakage fluid.
 19. The actuation device according to claim 18, wherein aseparation chamber is formed in a lower part of the housing extension.20. The actuation device according to claim 18, further comprising afluid sensor arranged in a lower part of the housing extension.
 21. Theactuation device according to claim 1, wherein the piston cylinder unitand the drive are spatially arranged at least partially adjacent orparallel and are arranged in one unit.
 22. The actuation deviceaccording to claim 1, wherein the piston arranged to be driven by thedrive is configured as an annular piston, a working chamber of which isarranged at least partially parallel to a further piston-cylinder unit.23. The actuation device according to claim 1, wherein working chambersof the piston-cylinder unit are connected via a hydraulic line, in whicha valve is connected.
 24. The actuation device according to claim 1,wherein suction valves are associated with delivery directions of thepiston.
 25. The actuation device according to claim 1, furthercomprising an auxiliary piston, a working chamber of which is connectedvia a hydraulic line to a travel simulator, and a changeover valvearranged in the hydraulic line, said changeover valve connecting theworking chamber of the auxiliary piston to that of the driven piston ina currentless manner.
 26. The actuation device according to claim 1,wherein a piston of the piston cylinder unit is arranged parallel to afurther piston of the piston cylinder unit, and wherein a solenoid valveis arranged in a hydraulic line connecting working chambers of thepistons.
 27. The actuation device according to claim 1, furthercomprising isolation valves are arranged in lines leading to wheelbrakes and suction valves arranged in lines leading to a reservoir. 28.The actuation device according to claim 1, wherein a free travel isprovided between the brake pedal or a pedal plunger and a spindle orbetween a coupling plunger and the spindle, wherein the spindle isconnected to the piston via a bending rod or a coupling.
 29. Theactuation device according to claim 1, further comprising a furtherpiston cylinder unit arranged parallel or concentrically to the pistoncylinder unit.
 30. A method for operating a brake device, wherein thebrake device comprises an actuating device having an electro-hydraulicdrive, a main piston-cylinder device configured to supply hydraulicpressure medium to brake circuits, a valve device configured to controlor regulate supply of the pressure medium, and an electronic control orregulating device, the method comprising: supplying pressure mediumvolume in a controlled manner to at least one brake circuit by means ofa further piston cylinder device, which is part of the actuating deviceand further includes a double-stroke piston, having a forward stroke anda return stroke, and at least one valve controlled by the control orregulating device, wherein an area of the double-stroke piston that iseffective at the forward stroke is of a different size from an area thatis effective at the return stroke, wherein the different areas are ableto be used for reduction of a piston force or a motor moment byconnecting the area effective at the return stroke with the areaeffective at the forward stroke by at least one valve.
 31. The methodaccording to claim 30, wherein a direct connection between first andsecond pressure chambers of the double-stroke piston is made by thevalve device, wherein the valve device comprises at least one valve,whereby the valve device is arranged without any other valves or othercomponents between the first and second pressure chambers and the valvedevice.
 32. The method according to claim 30, further comprisingactuating the valve device to thereby enable the double-stroke piston toprovide a continuous pressure increase by supplying pressure medium atthe forward stroke and the return stroke.
 33. The method according toclaim 30, further comprising pre-filling wheel brakes with pressuremedium at the beginning of braking by conducting corresponding volumeinto the brake circuit.
 34. The method according to claim 30, furthercomprising conducting pressure medium from a further piston-cylinderunit to the double-stroke piston by means of an auxiliary piston and avalve device.
 35. The method according to claim 34, further comprisingseparating, using a valve device, a travel simulator from a hydraulicconnection between the further piston cylinder unit and a brake circuit.36. The method according to claim 34, further comprising injectingvolume from the auxiliary piston via a piston and an open breather boreof the at least one brake circuit which is supplied with pressure mediumby the at least one piston.
 37. The method according to claim 34,further comprising detecting movement of the auxiliary piston by a slavetravel sensor.
 38. A brake device, comprising: an actuation device, anelectro-hydraulic drive, a main piston cylinder device arranged tosupply hydraulic pressure medium to brake circuits, a valve deviceconfigured to control or regulate a supply of the pressure medium, andan electronic control or regulating device (ECU), wherein the actuationdevice, the electro-hydraulic drive, the main piston cylinder device,the valve device and the ECU are configured to implement the methodaccording to claim 30, wherein the brake device further comprises a3/2-way solenoid valve having a downstream check valve and connected ina hydraulic line from the double stroke piston to the pressure chambersof the main piston cylinder unit or to brake circuit lines associatedwith said pressure chambers.
 39. The brake device according to claim 38,wherein, instead of the 3/2-way solenoid valve, a check valve isprovided in the hydraulic line from an auxiliary piston to the mainpiston cylinder device, and wherein, alternatively, an additionalcontrol of the check valve by means of a piston of a travel simulator ispossible, so that in the case of high pressures in the travel simulator,pressure to the double stroke piston is restricted.
 40. The brake deviceaccording to claim 39, wherein the auxiliary piston is arranged in aregion between the drive and the main piston cylinder unit and isconfigured as an annular piston.
 41. The brake device according to claim39, wherein the travel simulator is adaptive in terms of itscharacteristics and comprises at least two stages.
 42. The brake deviceaccording to claim 38, wherein the device comprises a modular structure,wherein the essential components of the device are combined in one(1-box) or in two assemblies (2-box).
 43. The brake device according toclaim 42, wherein, in the 2-box arrangement, the main piston cylinderunit and a travel simulator are combined in a first unit, and whereinthe drive and valves of a hydraulic control unit are combined in asecond unit.
 44. The method according to claim 30, further comprisingsupplying additional pressure medium volume in case of a system failure.45. The method according to claim 30, wherein pressure medium volume issupplied using a pressure signal or a motor current of the piston strokeand a pedal speed.
 46. The method according to claim 30, wherein bothpressure chambers of the double-stroke piston are connected to areservoir, whereby hydraulic volume from one or both chambers is able tobe released into the reservoir.
 47. The method according to claim 30,further comprising controlling one brake circuit using a multiplexmethod and controlling another brake circuit by inlet/outlet valves. 48.The method according to claim 47, wherein the controlling using themultiplex method and the controlling another brake circuit usinginlet/outlet valves comprises increasing pressure is increased in onebrake circuit and simultaneously decreasing pressure in the anotherbrake circuit using a further piston cylinder unit or outlet valves. 49.The method according to claim 30, further comprising, at a failure ofthe actuating device, supplying hydraulic volume by the further pistoncylinder device via the valve device into at least one brake circuitand/or a pressure chamber of the main piston cylinder device and therebyhydraulically moving the piston of the main piston cylinder deviceconfigured to transmit pressure to another brake circuit.
 50. A methodfor actuating a vehicle brake, comprising: driving a piston by anelectromotive drive of at least one piston-cylinder unit, wherein saidpiston is a double-stroke piston and is driven by the electromotivedevice to supply pressure medium to at least one brake circuit in acontrolled manner in both movement directions of the piston, forwardstroke and return stroke, and wherein the piston-cylinder unit includesat least a first pressure chamber and at least one second pressurechamber, the at least one first and at least one second pressurechambers being separated by the piston, wherein the at least one firstpressure chamber supplies pressure medium on the forward stroke and theat least one second pressure chamber supplies pressure medium on thereturn stroke, wherein an area of the piston that is effective at theforward stroke is of a different size from an area of the piston that iseffective at the return stroke; and controlling at least one valve suchthat the at least one first pressure chamber and the at least one secondpressure chamber are at least temporarily connected to each other toenable reducing a piston force or a motor moment.